I thought maybe it was 20th century Inca ruins, but it turns out to be (or so I'm told) the support frame for a reciprocating band saw from an early 1900's era sawmill.
The first shows ever so slight signs of camera shake due to low light, doesn't it? Still an interesting find there on the banks of "your" river.
But my favourite of all these is your #2!!!
Apart from the main COLOUR that it sports, I really like the elements of repetition, vanishing point and reflection here, as well as the "natural framing"!